For many years, oil and gas have been recovered from subterranean reservoirs through the use of drilled wells and production equipment. In many cases, it is desirable to utilize hydraulic fracturing techniques to improve primary and secondary recovery of oil and natural gas from the target reservoir. Hydrophilic polysaccharides and derivatized polysaccharides (such as guar gum, Carboxymethyl Hydroxypropyl Guar Gum [CMHPG], and Hydroxypropyl Guar Gum [HPG]) are often used to form viscosified fluids during hydraulic fracturing operations. These viscosified fluids are non-Newtonian and also can be cross-linked to give high gel strengths.
Following the well treatment operation, it is often desirable to retrieve the viscosified fluids from the wellbore. To promote flowback from the well, these viscosified fluids can be broken, or chemically degraded, to reduce the viscosity of the suspension. In many cases, “breakers” are introduced to facilitate and expedite the process of breaking the viscosified fluids. The loss of viscosity is typically the result of an oxidative/reductive chemical mechanism.
The oxidative/reductive degradation of the polysaccharide is commonly used to reduce the viscosity of the viscosified fluids. The oxidation of the polysaccharide is typically accomplished through a radical pathway in the presence of oxygen. Current oxidative type breakers frequently employ peroxide compounds slurried in a carrier fluid. Previously used carrier fluids have included hydrocarbon liquids such as diesel.
The use of a slurry of a powdered peroxide compound in a hydrocarbon liquid such as diesel has obvious safety problems. Hydrocarbon liquids such as diesel are combustible and flammable. Making and handling a slurry of an oxidizer in such a hydrocarbon liquid necessitates special handling procedures. In addition, slurries of powdered materials in these liquids do not exhibit long-term stability. The limited shelf life of these carrier fluids mandates that the breaker fluid be used promptly after the carrier fluid and oxidizer are mixed. Hydrocarbon liquids such as diesel can also be health and environmental hazards.
There is, therefore, a need for an improved oxidative breaker system that overcomes these and other deficiencies in the prior art.